Wat Chai Wattanaram, late Ayutthaya period
Interestingly, we have travelled around Thailand for some years, visited many temples and historical sites in the process. Only recently we were educated about the difference between Khmer and Thai (Ayutthaya) prang structures at temple compounts and religiously important sites (like Phimai and Phanomrung in Isaan province).
The prang was an important monument in Khmer and Ayutthaya architecture. Prangs can also be found in various forms in Sukhothai, Lopburi, Bangkok (Wat Arun). Sizes may vary, but usually the prangs measure between 15 and 40 meters in height, and resemble a towering corn-cob like structure.
Prangs essentially represent Mount Meru. In Thailand Buddha relics were often housed in a vault in these structures, reflecting the belief that the Lord Buddha is a most significant being in having attained enlightenment and having shows the path to enlightenment to others.
In Khmer structures, of course, Hindu deities were housed in the center of the prang monument.
The 'cella' or central (small) hall inside the prang, can be accessed through a porch, located in the east. With Thai (Sukhothai, Ayutthaya) architecture, the cella could often only be accessed by climbing stairs. Later on, the cella even disappeared in some prang structures, and was only suggested on the outside by niches (usually in the four important cardinal directions), where a Buddha image would be located. In Thai architecture, Garuda images were often present halfway the prang in four positions. Later on, they were omitted from the structure.
Now, what are differences between Khmer and Thai prangs. Well, to start with, the materials used to construct them would often be different. Khmer structures often used sandstone and laterite, if available in the area. Ayutthaya prangs were mostly built with bricks, then covered with stucco.
But the main visible difference is that Khmer built prangs taper off stepwise (in tiers of decreasing size). Ayutthaya prangs taper off gradually in a smooth way (without clearly visible steps). See examples below and above.
Prang at Wat Phutthai Sawan, early Ayutthaya period. 'Thai'-styled prang (rounded). The top of the prang tapers off gradually
Phra Prang Sam Yod, Lopburi - Three Khmer styled prangs. The size of the prang tapers off in steps towards the top
Khmer monument at Phimai, Nakhon Ratchasima province, Isaan, Thailand. Clearly, the central prang tapers off towards the top in steps